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Old 26th Nov 2004, 5:26 pm   #1
ChristianFletcher
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Default Radio alignment and goodness of valve sets

Can someone give advice on when radio alignment is necessary and typical faults this exhibits. Or should I just align everything that crosses my bench.

I have now restored quite a few radio sets, some have sounded better than other and alignment has not made any difference to performance. Are there measurement techniques to determine how good a set is, that don't rely on 50+ years of radio experience and a good ear. I am not old enough to know the sound of a new valve radio so its sometime difficult to judge if a set is faulty or just a poor performer. This especially related to distortion and sensitive of any newly acquired radio.
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Old 26th Nov 2004, 6:38 pm   #2
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Default Re: Radio alignment and goodness of valve sets

A properly aligned set should have good sensitivity at both ends of each waveband and dial calibration should be reasonably correct.

I don't know about domestic broadcast receivers, but the sensitivity of a Communications Receiver is generally given in the specification or sales leaflet in terms of Watts of Audio output for a given RF voltage at the aerial terminals. I am talking AM here, not FM.

For example 2 microvolts RF input for 100mW AF output. Also quoted may be the image rejection ratio (the level at which a signal spaced twice the IF from the wanted signal is received), IF rejection ratio (the level at which a signal on the IF frequency is received) and signal to noise ratio.

So given properly calibrated test gear you can measure your set's parameters and decide if it needs realigning!

In practice unless the set has been tampered with it should not be necessary to realign unless a frequency determining component such as a capacitor across an IF Transformer has been changed. Even then " tweaking " the affected circuit will generally suffice.

Having said that I must admit that I tend to realign everything. It generally makes no difference to performance. If have found that the IF circuits are genrally all tuned to the same frequency, but it may not be the correct one. RF and Oscillator circuits are more likely to be off tune than the IF.

So to realign or not to realign generally comes down to personal preference.

Graham.
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Old 26th Nov 2004, 9:56 pm   #3
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Default Re: Radio alignment and goodness of valve sets

Most times, if a set has not been tampered with, alignment should not be too far out. I have found that the age of the set can determine whether re-alignment would improve matters. For example most 1950's sets that I have restored, rarely need much alignment but older sets (a 1938 Philips for example) responded very well to alignment and sensitivity was greatly improved.

With any set that seems a bit 'flat', I generaly run a signal generator over it and this will generally (not always) improve things. Mostly the RF alignment can be improved, IF alignment not always.

Rich.
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Old 26th Nov 2004, 9:58 pm   #4
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Default Re: Radio alignment and goodness of valve sets

Christian,

I go through phases........

sometimes I align everthing that goes across the bench, others, only when I really need to.

The give aways for alignment, are, as Graham says, poor sensitivity (can you only hear half a dozen stations?), poor dial calibration (stations not where they should be), uneven sensitivity (you can here the whole world at one end of the band, but struggle to hear the next town at the other), distortion, and occasional image problems (you hear stations twice as you tune through the band, once at the correct point, and once 2x IF away).

However, for cases of distortion and sensitivity, always check the components of the radio first - are the valves good? are all the Rs and Cs in tolerance, even check the speaker is good and not binding or damaged (torn or distorted cone), before you get the signal generator out.

In truth, most old sets will benefit from re-alignment, if only to account for the changes in component value over the years, but most ears will not notice the difference, unless there was a serious fault. If you are being picky, you should re-align after changing RF, IF or FC valves, but on a domestic set the tolerances are so great that you won't notice the difference - in a communications reciever, where you're trying to get every last dB of signal / noise ratio, it can make a big difference when you change a valve (the inter-electrode capacitances vary between different valves with the same type number, and this can affect the tuning of associated circuits, especially at VHF).

Hope that helps.

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Old 27th Nov 2004, 2:40 pm   #5
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Default Re: Radio alignment and goodness of valve sets

I tend to realign sets as a matter of course.

One set had screwed plastic inserts to which ferrite slugs were glued. One of the slugs had come away and until that was glued back, the radio did all sorts of strange things.

I had a disaster with a Stella (Philips) set with a very neat looking MW tuning coil which contained a thing like a drinking straw around which the coil was wound. It just collapsed when I turned the adjuster, and I wished I hadn't messed.

With a few sets I've come across, someone had just 'had a twiddle' with the IFs. Occasionally, there's a set which has been carefully aligned to the wrong IF frequency.

Mostly, the cores come free after a soak with earex, and there's no problem.

The disadvantage of realigning is that you could break up a core, or core housing.

Domestic sets don't usually have published sensitivity figures. A way to estimate this aspect of performance is to compare a suspect set with a similar design which is known to be working properly.

Pete.
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Old 27th Nov 2004, 3:04 pm   #6
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Default Re: Radio alignment and goodness of valve sets

Thanks for the good advice.

I expect when you get more experienced with alignment the irregularities show up more easily.

Would a suitable check be to connect my signal generator to the aerial input. Inject a low level modulated signal so not to activate the radio AGC and measure output at the speaker. I could repeat this test over the frequency band. I guess in a perfect world the response at each spot frequency would be the same with a flat response across the band, this would show up any gross variation in sensitivity ?

I could also set the radio to mid band and vary the injected frequency, Would this enable me to plot the IF response, like using a wobulator. Would this be a useful thing to do.

Regards Chris.
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Old 27th Nov 2004, 6:17 pm   #7
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Default Re: Radio alignment and goodness of valve sets

Christian,

You can disable the AGC by earthing the AGC line with a jumper lead. Have a look at the circuit diagram before you do it, but I've never had any problems.

There's often a dropping off of local oscillator amplitude and corresponding dip in sensitivity towards the LF end of the shortwave bands, which was a common shortcoming. There's also the question of how accurately the local oscillator tracks the tuned signal.


Usually, with a domestic set, you peak up the IFs to the specified frequency and set them, then align the RF and local oscillator for each band and that's that. If you want to play about and with a set and study the response of the IF amp , the AGC and the local oscillator performance etc, it's interesting and you can learn a lot about how superhets actually work. From the point of view of taking an AM domestic radio and restoring it to its original performance, there is little to be gained.

Communication receivers with multi-stage IFs are another story. There may be published response curves for various bandwidths to be set up properly and a crystal filter to be tuned to. This really requires using a sweep oscillator and scope.

Pete.
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Old 29th Nov 2004, 9:24 am   #8
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Default Re: Radio alignment and goodness of valve sets

Thanks for the advice, I now know what to look out for. I think I will buy a cheap transistor radio to use as a reference.

I have found that on all my valve radio's I can get nothing on SW, Very little on LW and two sports channels on MW. Finding out what station I can receive would be useful before trying making comparisons.

Best regards Christian.
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Old 29th Nov 2004, 10:47 am   #9
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Default Re: Radio alignment and goodness of valve sets

Just an observation Christian.

You say that on all your valve sets you get nothing on shortwaves?

I think that unless you are living in a Faraday cage, shortwaves should be very lively . Most radio's will pick up a fair mix of shortwave stations during the day and will be positively 'crawling' with stations at night. Remember that an aerial is essential for shortwave reception.

I have several receivers with one or more shortwave bands and these are always lively.

Rich.

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Old 29th Nov 2004, 11:24 am   #10
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Default Re: Radio alignment and goodness of valve sets

Richard's right. You definitely need an aerial for SW.

Usually, 20ft of hook up wire running across the top of a bookshelf and connected to the A socket with a wander plug is plenty good enough.

Some valve radios have internal frame aerials, which work best for MW in my experience. I think they were mainly there because they enabled the set to be used without an untidy looking bit of wire hanging out of the back.

Pete.
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Old 29th Nov 2004, 11:32 am   #11
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Default Re: Radio alignment and goodness of valve sets

Quote:
Originally Posted by ChristianFletcher
I have found that on all my valve radio's I can get nothing on SW, Very little on LW and two sports channels on MW. Finding out what station I can receive would be useful before trying making comparisons.
As others have said, you should find stuff on SW, even with a few feet of wire as an aerial, but you will need an aerial of some sort. Short longwire aerials don't work well on LW, one of the reasons I built my external ferrite rod aerial, and you'll need a decent length of wire to get good reception even of R4 unless you live close to the transmitter. (This wasn't a problem when these radios were new, since everyone had an enormous longwire aerial in the garden).

It's probably a good idea to get hold of a small 50s valve set with a frame or ferrite rod aerial. This will give you a good idea what you should be receiving on LW and MW using a typical 5 valve set, if you used a decent aerial. This is quite similar to a 1960s MW/LW transistor set using germanium transistors (often not as good as a 70s set using silicon though).

HTH, Paul

Last edited by Paul Stenning; 26th Dec 2004 at 2:22 pm.
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Old 29th Nov 2004, 12:38 pm   #12
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Default Re: Radio alignment and goodness of valve sets

You make some good points.

Thinking back I do remember the SW band being full when I was younger living in another house, I now live in a valley in Holmfirth west Yorkshire very close to both Home moss and Emley transmitters. Tv reception is very poor and we cannot get channel 5.

I thought that radio reception was probably poor for these local geographical reasons. I will have to try a better aerial. I have at the moment 10m of wire strung from one end of the loft to the other. I can only really pick up two stations on MW and these come in incredibly powerful but are really the only thing on the band. My modern stereo in the house does not have LW or SW. I hope you guys are right and its just my poor Aerial.
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Old 29th Nov 2004, 1:28 pm   #13
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Default Re: Radio alignment and goodness of valve sets

I would be extremely surprised if location made much difference to shortwave reception unless you are living at the bottom of a mineshaft
A ten-metre aerial should be more than enough. You might want to try an earth, but I supect you may have " deaf " sets that may require some performance tweaking.
 
Old 29th Nov 2004, 1:41 pm   #14
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Default Re: Radio alignment and goodness of valve sets

Make that a lot of deaf sets ?
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Old 29th Nov 2004, 2:12 pm   #15
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Default Re: Radio alignment and goodness of valve sets

It's all very odd. A 10m loft aerial should be fine. SW reception varies throughout the day, but there's usually something especially at the HF end. Your valley location shouldn't affect SW very much. In the evening SW should be full of stations. You're some distance from Droitwich so will need a decent aerial for R4 (or RTE1 for that matter) but 10m should be OK.

The MW stations you can receive are probably coming from Moorside Edge near Huddersfield:
http://tx.mb21.co.uk/gallery/moorsideedge/index.asp

I'd suggest checking the aerial wiring for breaks and shorts, and checking what your roof is made of - some modern ceramic tiling material screens RF surprisingly well.

You could try building my external aerial - circuit is http://www.psherwin.demon.co.uk/ExtFerrite.jpg You should be able to build it in half an hour. BTW, it's more stable run on 3V.

Good luck, Paul
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Old 29th Nov 2004, 3:36 pm   #16
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Default Re: Radio alignment and goodness of valve sets

Christian,

I've just tried some quick and dirty tests feeding RF modulated at 30% and 400Hz into a Pye P76F via a .01 uF cap into the aerial socket.

Volume and tone set to max and roughly measured 100mW output. AGC left alone.

6mV @ 15MHz
4mV @ 7MHz
12mV @ 2MHz
15mV @ 1MHz
4mV @ .6MHz

The sig gen doesn't go down as far as LW and I couldn't be bothered to get one of the others out.

Even with just the frame aerial, it picks up a lot of MW, has no probs with R4 and picks up a few shortwave stations. The frequencies are more or less right. I sometimes had to tune around to find a quiet spot nearby, as I wasn't going to disconnect the frame aerial.

The Pye P76F is a fairly standard early 50s radio with ECH42, EF41, EBC41, EL41, EZ40.

Is it possible that your sig gen is way out of calibration and you've been carefully aligning sets to the wrong IF??

Pete.

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Old 29th Nov 2004, 4:21 pm   #17
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Default Re: Radio alignment and goodness of valve sets

I would still like to get a known "good radio" so that I can be sure there is no local anomaly. I must also check out the aerial problem and try Paul's improved aerial system.

It could also be that I have incorrectly setup some of the IFs on some of the sets, but this is not just one its on all my sets. I think that my signal generator Marconi TF2002-AS is almost certain out of cal, but I use it with a frequency counter and crystal calibrator, I am going to compare XTC's results with one of my sets, thanks for those figures very useful.

XTC: is the input measured at the radio side of your dummy aerial pad? and the power output figure across a resistive dummey load.

Paul: My roof is 4 inch thick stone slabs. I should probably add the wall are stone 36 inches thick. I had to try and core drill through to put in a kitchen fan - I gave up the stone was just to hard even using diamond drills. The roof timber are huge and made from Oak.

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Old 29th Nov 2004, 5:22 pm   #18
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Default Re: Radio alignment and goodness of valve sets

Quote:
Originally Posted by ChristianFletcher
Paul: My roof is 4 inch thick stone slabs.
Ahh. That sort of material will screen LW/MW/SW pretty effectively. I gathered from your website that you live in some sort of stone cottage, but I'd assumed the roof would be something like slate. I'm surprised the roof doesn't collapse if it's made of those sorts of materials.

I think you'll struggle with AM reception anywhere inside that sort of building. My amplified external ferrite rod isn't going to help much. As a test, try running a length of wire outside the building (though a window, say) and tying it to something above ground level - even running it along the wall will be some sort of test. I think you'll find your reception improves dramatically. Assuming this is so, you'll have to put up a proper external longwire aerial. This doesn't have to be up to amateur radio standards but the longer and higher you can make it, the better. Most people run them from under the eaves to something high at the bottom of the garden, like a tree or outbuilding.

It shouldn't matter much if you've aligned to the wrong IF frequency so long as everything's aligned to the *same* wrong frequency

Good luck, Paul

Last edited by Paul Stenning; 26th Dec 2004 at 2:24 pm.
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Old 29th Nov 2004, 5:37 pm   #19
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Default Re: Radio alignment and goodness of valve sets

Christian,

I connected the output of the sig gen to the cap via a scope probe on the x1 setting. I bent the other lead of the cap and pushed it into the aerial socket.

The output was measured from the meter in the sig gen which is an HP8640A. I've compared it with another 8640A and they were in good agreement, so I assume it's accurate. Maybe it should have been terminated properly, and I ought to have checked what the radio was being fed with a RF millivoltmeter - but I did say it was quick and dirty.

I measured the voltage across the speaker coil with a millivoltmeter.

Anyway, apart from whether the procedure was technically respectable or not, the P76 works pretty well, and if you do the same, I'd expect you to get more or less the same kind of figures for the same sort of set.

A comms receiver with its extra RF and IF stages should give that sort of output with a few microvolts of input.

If you've been aligning sets with a TF2002 and frequency counter you should be confident of the frequency and it's hard to imagine that the IFs have been aligned so far away from where they should be that it would make a difference.

One thing you could do is to take a set or two to a location outside the valley,and try them there with a simple wire aerial.

The other thing which may be possible, at least to try, is to rig up an outside long wire aerial.

Pete.
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Old 29th Nov 2004, 5:42 pm   #20
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Default Re: Radio alignment and goodness of valve sets

I think you must be right Paul / XTC. Now that I think about it when I go into the house my mobile goes from full strength to 1 bar or no signal. I usually stand infront of the window to make my calls. I cannot believe I had not thought of that before.

Thanks Chris.

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